This invention relates to an improved method of preparing polymeric acetal carboxylates, which are useful as complexing agents and detergency builders.
The property possessed by some materials of improving detergency levels of soaps and synthetic detergents and the use of such materials in detergent compositions is known. Such cleaning boosters are called "builders" and such builders permit the attainment of better cleaning performance than is possible when so-called unbuilt compositions are used. The behavior and mechanisms by which builders perform their function are only partially understood. It is known that good builders must be able to sequester most of the calcium and/or magnesium ions in the wash water since these ions are detrimental to the detergency process. However, it is difficult to predict which class of compounds possess useful combinations of builder properties and which compounds do not because of the complex nature of detergency and the countless factors which contribute both to overall performance results and the requirements of environmental acceptability.
Sodium tripolyphosphate (STPP) has been found to be a highly efficient cleaning and detergency builder and this compound has been widely used for decades in cleaning formulations. Indeed, millions of pounds of STPP are used each year in cleaning formulations because of its superior builder qualities. However, because of the recent emphasis on removing phosphates from detergent and cleaning compositions for environmental reasons, the detergent and cleaning industry is now looking for materials suitable for use as builders which do not contain phosphorus and which are environmentally acceptable.
Polymeric acetal carboxylates have been found to be suitable as a replacement for STPP in detergent compositions. The composition of such polymeric acetal carboxylates has been disclosed in U.S. Pat. No. 4,144,226 issued Mar. 13, 1979 and in Ser. No. 962,512 filed Nov. 20, 1978. The use of such polymeric acetal carboxylates in detergent compositions is disclosed in U.S. Pat. No. 4,146,495 issued Mar. 27, 1979. A preferred method for the saponification of the esters of the polymeric acetal carboxylates to form the corresponding alkali metal salt is disclosed in U.S. Pat. No. 4,140,676 issued Feb. 20, 1979. The polymeric acetal carboxylate salts described in the above applications and patents were tested for sequestration function using the procedures described by Martzner et al in "Organic Builder Salts as Replacements for Sodium Tripolyphosphate", TENSIDE, 10, No. 3 pg. 119-125 (1973). As a result of such tests, the polymeric acetal carboxylate salts were found to be superior detergent builders compared to STPP, and were stable under laundry use conditions but depolymerized at lower pH making the polymers more readily biodegradable.
Although the methods for preparing polymeric acetal carboxylates disclosed in the above patents and patent applications are satisfactory, it was surprisingly found that the acetal carboxylates could be stabilized by chemically stable groups derived from an acetal according to transacetalization reactions. The reaction of an alcohol with an acetal by transacetalization using phosphorus pentoxide or molecular sieves to remove alcohol to shift the equilibrium toward completion is known to the art (see for example SYNTHESIS, 1975, pages 276-277, and SYNTHESIS, 1976, page 244).
While such reactions may be known to the art, their successful application to the stabilization of polymeric acetal carboxylates was surprising because of the likelihood of side reactions including the depolymerization of the polymeric acetal carboxylate. In addition, the method of the present invention provides a variety of new terminal structures which could not be readily produced by previously known methods of stabilization.